The present invention relates generally to a method of fabricating a large area multielement contactor and, more particularly, to a method of mounting multiple contactor units on a support substrate with precise alignment.
Modern integrated circuits include many thousands of transistor elements with many hundreds of bond pads disposed in close proximity to one another (e.g., 5 mils center-to-center). The layout of the bond pads need not be limited to single rows of bond pads disposed close to the peripheral edges of the die (see, e.g., U.S. Pat. No. 5,453,583). The proximity and number of pads is a challenge to the technology of probing devices.
Semiconductor devices are generally fabricated on a wafer of silicon, with many devices on a single wafer. Modern technology uses 8-inch (200-cm) wafers, and is moving to 12-inch (300-cm) wafers. Essentially every single device fabricated on a wafer needs to be tested by probing. Probing more than one device at a time is particularly advantageous.
Modern probing equipment can probe 32 or more semiconductor devices at the same time.
However, this is only a small fraction of the total number of die on a wafer. There has been great interest in developing a probing system that can contact more, preferably all die on a wafer at the same time.
Generally, previous attempts at implementing schemes for partial or full wafer-level testing have involved providing a single test substrate with a plurality of contact elements for contacting corresponding pads on the wafer being tested. This may require extremely complex interconnection substrates and may include as many as tens of thousands of such contact elements. As an example, an 8xe2x80x3 wafer may contain 500 16 Mb DRAMs, each having 60 bond pads, for a total of 30,000 connections. In one representative embodiment, there are 30,000 connections between the wafer under test (WUT) and the test electronics. Moreover, the fine pitch requirements of modem semiconductor devices require extremely high tolerances to be maintained when bringing the test substrate together with the wafer being tested.
To effect reliable pressure connections between contact elements and, e.g., a semiconductor device, one must be concerned with several parameters including, but not limited to: alignment, probe force, overdrive, contact force, balanced contact force, scrub, contact resistance, and planarization. A general discussion of these parameters may be found in U.S. Pat. No. 4,837,622, entitled HIGH DENSITY PROBE CARD, incorporated by reference herein, which discloses a high density epoxy ring probe card including a unitary printed circuit board having a central opening adapted to receive a preformed epoxy ring array of probe elements.
A more sophisticated probe card uses resilient spring elements to make contact with a device on a wafer. Commonly assigned parent application Ser. No. 08/789,147, now U.S. Pat. No. 5,806,181, entitled xe2x80x9cContact Carriers for Populating Larger Substrates with Spring Contactsxe2x80x9d, issued Sep. 15, 1998, discloses such a probe card in connection with what in that patent is FIG. 5, which is reproduced in this disclosure as FIG. 1A.
FIG. 1A illustrates an embodiment of a probe card assembly 500 which includes as its major functional components a probe card 502, an interposer 504 and a space transformer 506, and which is suitable in use for making temporary interconnections to a semiconductor wafer 508. In this exploded, cross-sectional view, certain elements of certain components are shown exaggerated, for illustrative clarity. However, the vertical (as shown) alignment of the various components is properly indicated by the dashed lines in the figure. It should be noted that the interconnection elements (514, 516, 524) are shown in full, rather than in section.
The probe card 502 is generally a conventional circuit board substrate having a plurality (two of many shown) of contact areas (terminals) 510 disposed on the top (as viewed) surface thereof. Additional components (not shown) may be mounted to the probe card, such as active and passive electronic components, connectors, and the like. The terminals 510 on the circuit board may typically be arranged at a 50-mil pitch. The probe card 502 is suitably round, having a diameter on the order of 12 inches.
The interposer 504 includes a substrate 512. Resilient interconnection elements 514 are mounted to and extend downward (as viewed) from the bottom (as viewed) surface of the substrate 512. Resilient interconnection elements 516 are mounted to and extend upward (as viewed) from the top (as viewed) surface of the substrate 512. Various spring shapes are suitable for the resilient interconnection elements 514 and 516. These elements preferably are composite interconnection elements with a soft core and hard shell. In another preferred embodiment, the resilient interconnection elements comprise a resilient material in a resilient shape. In one preferred embodiment, tips of interconnection elements 514 and 516 are at a pitch that matches that of the terminals 510 of the probe card 502.
The interconnection elements 514 and 516 are illustrated with exaggerated scale, for illustrative clarity. In certain preferred embodiments, the interconnection elements 514 and 516 extend to an overall height of 20-100 mils from respective surfaces of the interposer substrate 512.
The space transformer 506 includes a suitable circuitized substrate 518, such as a multilayer ceramic substrate having a plurality of terminals 520 disposed on the lower (as viewed) surface thereof and a plurality of terminals 522 disposed on the upper (as viewed) surface thereof. The terminals suitably may be contact areas or pads, or other structures known in the art. In this example, the lower plurality of contact pads 520 is disposed at the pitch of the tips of the interconnection elements 516 (e.g., 50 mils), and the upper plurality of contact pads 522 is disposed at a finer (closer) pitch (e.g., 25 mils). These resilient interconnection 514 and 516 elements are preferably, but not necessarily, composite interconnection elements.
A plurality of resilient interconnection elements 524 are mounted directly to the terminals 522 and extend upward (as viewed) from the top (as viewed) surface of the space transformer substrate 518. The resilient interconnection elements function as probes or probe elements. As illustrated, these resilient interconnection elements 524 are suitably arranged so that their tips (distal ends) are spaced at an even finer pitch (e.g., 5 mils) than their proximal ends, thereby augmenting the pitch reduction of the space transformer 506. These resilient contact structures (interconnection elements) 524 are preferably, but not necessarily, composite interconnection elements.
A problem associated with an array of contact elements, including spring contacts, is that often the terminals of an electronic component are not perfectly coplanar or are not aligned in an X-Y direction or in angular rotational direction with the contact pad. Contact elements lacking in some mechanism incorporated therewith for accommodating these xe2x80x9ctolerancesxe2x80x9d (gross non-planarities) will be hard pressed to make consistent contact pressure contact with the contact pads of the electronic component.
Heretofore, it has been difficult and expensive to fabricate an assembly of contact elements of arbitrary size or shape to reliably make contact with the terminals of devices having a large size or an unusual shape.
Briefly stated, a method of manufacturing a contactor is provided wherein a plurality of contactor units is mounted on a support substrate such that contact elements attached to the contactor units align with a plurality of contact pads on a device. More particularly, a method of fabricating a segmented contactor according to the present invention comprises the steps of providing a support substrate, providing a contactor unit having a first plurality of electrical contact elements on a first surface thereof, providing and using an adjustment region to selectively position the contactor unit relative to the support substrate, and securing the contactor unit to the support substrate.
In the preferred embodiments, the contactor providing step includes providing a plurality of contactor units, the providing and using an adjustment region step includes selectively positioning the plurality of contactor units relative to the support substrate, and the securing step includes securing the plurality of contactor units to the support substrate.
Preferably, the electrical contact elements are coplanar across the plurality of contactor units. The contactor providing step can further include the steps of providing a second plurality of electrical contact elements on a second surface of the contactor unit and selectively positioning and securing the second electrical contact elements to the first electrical contact elements.
In one preferred embodiment, the securing step includes using a joining material that is malleable at an elevated temperature. The joining material is fixed into position at the elevated temperature. This allows the contactor units to self-align during reflow of the joining material interconnecting the contactor units and the support substrate. In alternative embodiments, alignment facilitation devices are utilized to assist the self-alignment of the contactor units during a malleable state of the joining material.
According to one particular implementation of the invention, probe elements such as spring contacts are pre-fabricated on individual spring contact carriers (xe2x80x9ccontactor unitsxe2x80x9d or xe2x80x9ctilesxe2x80x9d). A number of these contactor units are mounted to a support substrate in a defined relationship with one another, preferably so that the tips of the spring contacts are coplanar with one another. The contactor unit substrates are preferably relatively inexpensive and conducive to successfully yielding spring contacts.
As used herein, the term xe2x80x9cprobe elementxe2x80x9d includes any element such as a composite interconnection element, spring contact, spring element, contact bump, or the like, suited to effect a pressure connection to terminals (e.g., bond pads) of an electronic component (e.g., a semiconductor die, including unsingulated semiconductor dies resident on a semiconductor wafer). A probe element also may be a terminal or receptacle to receive a resilient contact element to effect a pressure connection to terminals, e.g. springs, of an electronic component.
As used herein, the terms xe2x80x9ccontactor unitxe2x80x9d or xe2x80x9ctilexe2x80x9d includes any component having probe elements on a surface thereof, a plurality (preferably identical) of which can be mounted to a larger substrate, thereby avoiding fabricating the probe elements directly upon the larger substrate.
As used herein, the term xe2x80x9ccontactor unit substratexe2x80x9d includes a solid substrate (e.g., see 100 in FIG. 4A) or the like.
As used herein, the term xe2x80x9ca larger substratexe2x80x9d is any substrate having a surface on which a plurality of contactor units can be mounted. Generally, a number of contactor units would be mounted to the larger substrate, dictating that the surface area of the larger substrate would be much larger than the surface area of an individual contactor unit. This specifically includes the interconnect substrate of a probe card assembly.
According to a feature of the invention, a plurality of contactor units having spring contact elements fabricated on a surface thereof can be fabricated from a single, inexpensive substrate such as a ceramic wafer, which is subsequently diced to result in a plurality of separate, preferably identical contactor units which can be individually mounted to the surface of an interconnect substrate.
An advantage to the technique of using contactor units, rather than fabricating spring elements directly upon the surface of the electronic component is that the electronic component is readily reworked, simply by replacing selected ones of the one or more contactor units attached/connected thereto.
It is an object of the present invention to provide a contactor that overcomes the drawbacks of the prior art described above.
It is another object of the present invention to provide a method of fabricating a contactor that overcomes the drawbacks of the prior art described above.
It is a further object of the present invention to provide a method of mounting contactor units on a contactor such that the contactor units align with semiconductor devices resident on a product wafer.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings.